Liquid crystal display devices (LCDs) have many advantages, such as thin body, non-radiation, and power saving, so that they are widely used. Generally, a liquid crystal display pane includes a color filter (CF) substrate, a thin film transistor (TFT) array substrate, and liquid crystal disposed between the CF substrate and the TFT array substrate. The directions of the liquid crystal molecules are changed by providing the power to the TFT array substrate or not, and then lights of a backlight module are projected to the CF substrate to produce images. The property and performance of the TFT array substrate are most dependent upon the materials forming each element of the TFT array substrate. Metal conducting wires are arranged on the TFT array substrate, and the metal conducting wires are made by etching a metal layer on the TFT array substrate by a physical vapor deposition (PVD) method. The etching processes includes a dry etching process and a wet etching process.
A common metal conducting wire used in the TFT array substrate is an aluminum conducting wire. However, with the development of the liquid crystal display (for example a television) trending and requiring a large size, high resolution, and high speed driving frequency, technical personnel in the liquid crystal display field face a problem: a resistance-capacitance (RC) delay time caused by the resistance of the TFT array substrate. Because the aluminum conducting wire has a higher resistance rate, a pixel electrode layer of the TFT array substrate cannot be charged completely; moreover, with HI-FAS (high frequency amplitude selection: greater than 120 Hz) liquid crystal displays being widely used, the above-mentioned phenomenon is more obvious. Compared with the aluminum conducting wire, a copper conducting wire has a lower resistance rate and a better electromigration resistance ability, so as to be used on the TFT array substrate to solve the above-mentioned problem caused by the aluminum conducting wire.
An adhering property between copper and glass is poor, so it is necessary to use an under bump metal layer to be transited. Furthermore, when above 200° C., copper easily reacts with silicon to produce a chemical compound including copper-silicon (CuSi3) by an inter-diffusion effect. That is, copper will react with a semiconductor layer of the TFT array substrate to produce a very high contacting resistance, so that it is also necessary to use another under bump metal layer to be transited. Nowadays, a common method is to use a refractory metal to be a transitional adhesive layer or barrier layer, such as molybdenum (Mo), titanium (Ti), alloy with corresponding elements, etc. However, after an etching process, different metals or alloys of barrier layers form different profiles. For example, when stripping a photoresist, a contacting edge between a copper and a molybdenum produces a hollow phenomenon, forming a crack. This hollow phenomenon will cause a short circuit in a source electrode, a drain electrode, or a gate electrode, so that the yield of the display terminal is influenced, obviously.
Refer now to FIG. 4, which is a schematic cross-sectional view showing in a conventional manufacturing method for an array substrate, the whole of a structure of a gate electrode layer 13 and a first metal layer 12 are covered with a gate electrode insulation layer 15. As shown in FIG. 4, in the conventional technology, there is a crack 14 on a contacting edge between the gate electrode layer 13 and the first metal layer 12 on a base substrate 11.